Bathroom Condensation and Black Mould Problems

How to prevent bathroom black mould

At VapourFlow we are often asked for advice on how to eliminate bathroom black mould caused by excessive condensation. This is a typical example of the type of question we receive:

“Could you please advise on what would be an appropriate solution for the 3 bathrooms detailed below. All of them have ceiling extractors fitted by the builders but all are ineffective and we get black mould on the ceiling and walls within a couple of months of cleaning/decorating.

Main bathroom (bath, shower, sink & toilet) approx 10ft x 8ft with a window.

En-suite bathroom (bath, shower, sink & toilet) approx 9ft 6ins x 10ft 6ins – no window or other ventilation.

En-suite – shower, sink & toilet only approx 10ft 6ins x 3ft 6ins – no window or other ventilation.

The distance from the fan to the external wall is approx 20ft.”

What we would recommend is as follows:

The best practice ventilation solution for each of the three bathrooms is the Dryvent B.  The Dryvent B bathroom fan is a high performance dehumidifying extractor fan designed for particularly demanding condensation control requirements of bathroom environments, and it is particularly effective for use in properties suffering from damp conditions and black mould.

The Dryvent B continually extracts on low speed to remove moisture laden air at source before it can condense so an added benefit is that this background level of ventilation also improves the air quality throughout the property.

Condensation control is achieved through the inclusion of an internal, microprocessor driven Autostat humidistat unit. When the built-in Autostat humidistat detects the humidity level rising above acceptable levels the fan triggers into high speed delivering powerful performance when it is needed most.

Some other factors would be worth considering in order to control condensation and mould:

Check the ceiling material and the surface coat. Anaglypta type (embossing around woodchip with epoxy glue ) wallpaper should not be used as this is “food for black mould”.  It is important to use specific bathroom paints that have anti-fungicidal properties that are repellent to water vapour.  These can be found in any high street DIY store.
The cooler the surface the more it attracts moisture from other areas which then rapidly turns vapour in to condensate as the dew point is reached, and you get condensation and then black mould.   So it is important to ensure that the ceilings are well insulated!
Apart from localised ventilation other major sources of moisture need consideration.  If you have extractor systems in the kitchen and utility rooms that take the locally produced moisture out of the dwelling then these will need to extract to current building regulation rates and preferably be automatic.

10 thoughts on “Bathroom Condensation and Black Mould Problems

  1. Peter says:

    Ray, I live in a bungalow with the bedrooms in the roof space. At the edge of each room there are plasterboard walls with a hatch to create a small attic space. The bed is up against one of these walls which is not insulated and I can see mould (black spots) appearing on the wall. The opposite wall has no such problem and is perfectly dry.

    Will it help if I insulate behind the plaster board wall to prevent the rapid change in temperature?

    • Ray says:

      Hi Peter
      The bed is insulating the wall and reducing air circulation, as a result the plaster wall is the coolest surface and attracting moisture, forming condensate and then your mould.
      Insulating behind the plaster board will help; you will also need to pull the bed away from the wall to allow this surface to warm up.
      As you are getting mould the likely of reoccurrence is high, it is important to remove all mould as soon as possible, also you will need to consider where the moisture is coming from – Kitchen/Bathroom Are they ventilated?

  2. Ray says:

    Really good to have your positive comments, will encourage me/us to do some more.
    If we can be of any help with condensation damp – let us know, cant help your work tho

  3. ariuna says:

    Dear All,

    I am really straggling to encourage tenants to open the downstairs bathroom window. However it has been ongoing problem and I really would like to know what I can do to prevent mould growing. It has been proved that tenants will never be reliable and we can not prove that tenants open the windows either. I have lived in that house over 2 years without exctractor fan and never had a problem. However the bathroom now has exctractor fan but still no luck. Help!!!

    Thank you so much for any ideas you can recommend me.


    • Ray says:

      Dear Ariuna
      The issue with opening bathroom windows is a universal issue and occurs with home owners as well particularly ground floor where privacy and security are more of a concern.
      The solutions is the use of a condensation control ventilator such as the Dryvent B this will trickle vent at all times then go to Automatically to high level extract when the air moisture levels increases, a simple extractor fan is not enough!.
      Following the installation of the correct ventilation system you will need to ensure all mould is removed and the surfaces redecorated with suitable bathroom paints. Note: The kitchen will also require an extractor fan = Wolf K as a lot of water production in the house comes from cooking/washing etc. If not checked the kitchen’s nascent moisture will readily migrate to the cooler bathroom area.

  4. Maria says:

    Dear Ray, my bathroom is 6′ 7 x 5′ and does have a window that opens. The current extractor, which needs replacing, is right above the shower. The bathroom gets very steamy after a shower so the extractor is not really doing its job very well and black spots have appeared on the ceiling a few months after retiling & painting the bathroom and installing a new power shower. So, 2 questions: which of your extractors would work best in the space and where, ideally, should the new extractor be sited? I could move it to the right of where it is now so it is just on the opposite side of the shower screen to where the shower is located, or should I just replace over the old extractor?

    • Ray says:

      Dear Maria
      The issue you describe with spot mould appearing following retiling is due to the new tiled surface repelling the moisture and the droplets slowly evaporating providing ideal conditions for mould to develop and multiply, without a ventilation résumé that you have correctly identified the mould would affect the grout (even grout with and mould properties) after about a year, additionally the mould spores would flow in the air increasing mould spoor levels to other parts of your properties, naturally you breath in the mould and your body deals with this however increasing mould presence will increase your susceptibility to bronchial issues as your body defences fight these invasive spoor levels. This you probably know however worth mentioning for other readers.
      The best solution is a very low powered ventilation fan running continuously and then automatically switching to high power/higher extract rate when moisture levels increase in the air due to showering etc. Our product for this is the Dryvent B, this can be seen under bathroom fans on our products page, also available through the Buy button on our website.
      Regards, Ray

  5. sue atkins says:

    ray i have the same problem as maria ( october 14 2011 1 58 pm ) , could my husband install your product the dryvent b or would it require a professional builder/electrician

    • Ray says:

      Dear Sue
      The fitting of a fan is not a complex task; however some regulations need to be considered for your safety:
      The fitting of our Dryvent fans requires a hole to the outside; the fan spigot size is 100mm, to core drill or pin drill through the brickwork the diameter of the hole should be around 112mm to allow for a wall sleeve.
      Note: the installation will need to be at high level and should not be below the shower head
      The electricity supply needs to be RCD (residual current device) protected, you may already have one at the power distribution board in your home (fuse box), if you do not they are readily available at DIY stores and Electrical wholesalers, the RCD to be rated at no more than 30 mA.
      Regulations apply for home electrical connections:
      Please see Health and safety executive website –
      The bottom line is that you need a person qualified with a Part P certificate (minor works certificate) to place a new electrical supply circuit in your home.
      Thank you for your enquiry

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